Electrostatic spray painting apparatus



Nov. 15, 1960 Filed June 24, 1958 F. A. CROSKEY ET AL ELECTROSTATICSPRAY PAINTING APPARATUS 2 Sheets-Sheet l INVENTORS 55022 @(Imsgg, e

B Y 65.474225 Q ZZZ??? Nov. 15, 1960 F. A. CROSKEY ETAL 2,960,273

ELECTROSTATIC SPRAY PAINTING APPARATUS Filed June 24, 1958 2Sheets-Sheet 2 if {HE ELECTROSTATIC SPRAY PAINTING APPARATUS Frank A.Croskey, New Baltimore, and Charles D. Tuttle,

Wyandotte, Mich, assignors to General Motors Corporation, Detroit,Mich., a corporation of Delaware Filed June 24, 1958, Ser. No. 744,189

4 Claims. (Cl. 239-15) This invention relates to electrostaticspray'painting apparatus, and more particularly to electrostatic spraypainting apparatus wherein spray emitting means, as a spray gun, emits aspray of atomized particles along a path directed through anelectrostatic field.

One feature of the invention is that it provides improved electrostaticspray painting apparatus; another feature of the invention is that itprovides electrostatic spray painting apparatus including spray emittingmeans for directing a spray of atomized particles along a path anddischarge electrode means and collector electrode means, both located onthe same side of the path of atomized particles emitted by sprayemitting means; yet a further feature of the invention is that thecollector electrode comprises a conductive cylinder located in spacedrelation to the discharge electrode means and to the spray emittingmeans on the same side of the path of spray as the discharge electrodemeans; still another feature of the invention is that it providesdischarge electrode means located in spaced relation to the sprayemitting means in the direction in which spray is emitted therefrom andon one side of the path of the spray and a collector electrode locatedin spaced relation to the discharge electrode means and to the sprayemitting means generally opposite the spray emitting portion thereof andon the same side of the path of spray as the discharge electrode means.

It is well known in the prior art to use a spray painting apparatus inwhich a pneumatic spray gun emits a spray of atomized particles throughan electrostatic field created between a discharge electrode having aplurality of pointed members and a broad flattened collector electrode.The discharge electrode and the collector electrode are located onopposite sides of the path of spray so that the atomized particles passthrough the field in a direction generally transverse to the directionof extent of the lines of force therein.

When using such prior art apparatus, the high intensity field existingbetween the discharge electrode and the collector electrode creates anelectric wind which tends to force the atomized particles back towardthe spray gun with the result that higher pneumatic pressures arerequired than would otherwise be necessary to atomize the paint and blowit through the field. Additionally, the paint tends to collect on thebroad flattened collector electrode. This is due in part to therelatively large surface expanse of the collector electrode and in partto the location of the collector electrode with reference to thedischarge electrode and the gun. When a quantity of paint has beendeposited on the collector electrode, it is necessary to clean theapparatus in order to prevent the formation of paint stringers extendingfrom the collector electrode toward the discharge electrode. Suchstringers would shorten the air gap of the field and increase the fieldintensity with the resultant danger of arcing. In the use ofelectrostatic apparatus of this general type, it has been determinedthat a field intensity of the order of 13 kv. per inch provides theStates Patent ice greatest efliciency; for example, when utilizing avoltage of the order of 40 kv., it is preferable to space the dischargeelectrode and the collector electrode a distance of about three inchesfrom each other. The build-up of paint stringers on the collectorelectrode efiectively changes this spacing and may result in danger ofarcing.

The invention disclosed and claimed herein provides improvements oversuch prior art apparatus by locating both the discharge electrode andthe collector electrode on the same side of the path of spray emittedfrom the spray gun. This modifies the efiect of the electric windcreated by the field, whereby the area of greatest intensity of theelectric wind is not directed against the atomized particles but is outof the path of movement of the atomized particles. Furthermore, sincethe particles are not moved transversely through the field, i.e., arenot moved between the two electrodes-the collector electrode does notaccumulate an excessive amount of paint so that it is not necessary toclean the apparatus frequently, nor is there the likelihood that enoughpaint will build up on the collector electrode to form paint stringersfeeding out into the field.

These and other features of the invention will be apparent from thefollowing description and from the drawings, in which:

Fig. 1 is a plan view of an electrostatic spray painting installationincluding the new apparatus;

Fig. 2 is an enlarged view of a portion of the apparatus of Fig. 1;

Fig. 3 is a side elevation taken along the line 3-3 of Fig. 2;

Fig. 4 is a detail section taken along the line 44 of Fig. 3 and showingthe discharge electrode arrangement; and

Fig. 5 is a detail section through the discharge electrode taken alongthe line 5-5 of Fig. 3.

Referring now more particularly to the drawings, a conventional conveyor10 mounts a plurality of hangers 12 which carry a succession ofworkpieces 14 which, for example, may be automobile window garnishmoldings. These workpieces are moved in succession past theelectrostatic spray apparatus described below. A mounting stand 16carries a yoke 18, the height of which may be adjusted by a clampingdevice controlled by a hand wheel 20. From the yoke 18 a mounting rod 22projects angularly upwardly, and at its top end is secured to a metallichousing bracket 24. A clamping device controlled by turn handle 26 isprovided for adjustment of the angular relationship between the mountingrod 2 2 and the housing bracket 24. A conventional pneumatic spray gun28 is mounted on the housing bracket 24 and terminates at its forwardend in a conventional atomizing spray nozzle 30 which is directed towardthe workpieces which pass on the conveyor. The gun 28 is connected by atube 32 to a source of paint and is connected by a tube 34 to a sourceof compressed air so that during operation paint is atomized and emittedfrom the spray gun 28 as shown at 36 along a path directed toward aworkpiece 14 on the conveyor. The atomized paint is dispersed in anexpanding fan-shaped pattern.

At one end the housing bracket 24 is formed with an integral generallycylindrical support sleeve 24a having a longitudinal bore in which ismounted an insulating tube 40 which may be of nylon. This tube extendsforwardly a distance about four inches beyond the end of the housingsleeve 24a and at its free end it carries a discharge electrodeassembly. The assembly comprises a plurality of elongated pointedneedle-like conductor members 42 which may be No. 1/0 steel darningneedle. In the illustrated embodiment of the invention there are sevenof these needles arranged in a fan-shaped array and all connected, as bysoldering to a base member 44 which may be formed of brass wire. Thebulk of the body portion of the pointed discharge electrode members andthe entire base 44 upon which they are mounted are molded as a unit intoan insulating casing 45 which may be formed of epoxy resin and thepointed end of each electrode member projects out of the casing.

As shown in Fig. 5, the base member 44 is attached to a connector 46which extends into the bore of the nylon tube 40 and in turn isconnected to a lead wire 48 which at its other end is connected to asource of high voltage in a power supply 50. Although the power supply50 is not shown in detail, it is of conventional construction, includinga high voltage developing means and a low voltage return arrangement,and preferably, is arranged to deliver a voltage output of the order of40 kv.

On the same side of the gun 28 as the discharge electrode means thereare formed upper and lower bosses 24b and 24c which respectively mountmetallic holding rods 52 and 54 upon which is clipped a conductivecollector electrode comprising an elongated metallic cylinder 56. In apreferred construction of the invention, the collector electrode 56comprises a brass tube having an overall length of about seven inches,an inner diameter of 3 inch, and an outer diameter of 1 inches. The tubeis formed with spaced key slots for the reception of buttons formed onthe ends of the rods 52 and 54 so that the tube is removably mounted onthese rods.

It may be seen from an examination of Figs. 2 and 3 that the dischargeelectrode means, which are electrically insulated from the spray gun bythe tube 40, are located in spaced relation thereto in the generaldirection in which spray is emitted and on one side of the path of thespray. Furthermore, the pointed needle-like members 42 are arranged in afan-shaped array lying in a plane perpendicular to the plane of thefan-shaped spray pattern emitted by the spray gun. The needle-likedischarge electrode members are arranged perpendicular to the directionof movement of the spray particles and point toward the plane of thefan-shaped spray pattern. The collector electrode 56 is located inspaced relation to the discharge electrode means and to the spray gun.Preferably the distance between the discharge electrodes and thecollector electrode is about three inches, and preferably a voltage ofthe order of 40 kv. is used so that the field intensity be tween thedischarge electrode and the collector electrode is of the order of 13kv. per inch. The collector electrode is also spaced from the nozzle orpaint emitting end portion 30 of the spray gun and is generally oppositethe nozzle on the same side of the path of spray as the dischargeelectrodes. The axis of the cylindrical collector electrode istransverse to the axis of the spray gun 28 and is generally transverseto the axis of the center one of the pointed discharge electrode membersas shown best in Fig. 3. Furthermore, the axis of the collectorelectrode preferably is parallel to the plane of the fan-shaped spraypattern. The collector electrode is electrically connected to the spraygun through the rods 52, 54 and the support bracket 24, and theseelements are connected to the ground return portion of the power supplythrough a wire 60. If desired, the spray gun 28 and the collectorelectrode 56 may be grounded or these elements may be a relatively fewvolts (as 80 or 90 volts) above ground if the ground return circuitincludes a low voltage developing means.

In operation, paint is atomized and sprayed from the nozzle 30 of thespray gun 28 under a relatively low pressure of a few pounds per inch toform an expanding fan-shaped spray directed in a path toward workpiece14 as it passes on the conveyor 10. A high voltage electrostatic fieldis developed between the discharge electrodes 42 and the collectorelectrode 56. This field is defined by a plurality of lines of force ofelliptical shape extending between the two electrodes so that the pathof paint spray is through the field, whereby the paint particles arecharged as they pass through the field and are attracted to workpieceson the conveyor, which workpieces preferably are grounded. Normally thedischarge electrodes are maintained at a negative potential. Since thedischarge electrode and the collector electrode are both located on thesame side of the spray gun, the greatest intensity of electric windcreated by the electrostatic field between these electrodes is not inopposition to the moving atomized particles, and in fact the path ofmovement of these particles does not bring them into contact with theelectric wind of greatest intensity. In fact, the electric wind whichexists in that part of the field intersecting the path of movement ofthe particles, when combined with the direction of particle movement insaid path, results in a force vector which will carry the particlesawayfrom the electrodes. Furthermore, by virtue of the cylindrical shapeof the collector electrode and by virtue of its location generallyopposite the nozzle 30 from which the atomized particles are emitted,the collector electrode does not receive any substantial amount ofpaint. Con sequently, it is not necessary to shut down the apparatusfrequently for cleaning, nor is the arrangement conducive to thecollection of enough paint on the collector electrode to develop paintstringers extending from the collector electrode towards the dischargeelectrodes to change the field strength and increase the possibility ofarcing. The intense field between the two electrodes insures chargingpaint particles moving in a path through this field to provide aneffic-ient electrostatic painting arrangement.

While we have shown and described one embodiment of our invention, it iscapable of many modifications. Changes, therefore, in the constructionand arrangement may be made without departing from the spirit and scopeof the invention as set forth in the appended claims.

What is claimed is:

1. An electrostatic spray painting apparatus, comprising, incombination, a support, spray emitting means mounted on said support foremitting a spray in a path, discharge electrode means mounted on saidsupport and electrically insulated from said spray emitting means, saiddischarge electrode means being located in spaced relation to said sprayemitting means in the direction in which the spray is emitted therefromand on one side of and adjacent to the path of the spray, a collectorelectrode mounted on said support in spaced relation to said dischargeelectrode means and adjacent to said spray emitting means, saidcollector electrode being located on the same side of and adjacent tothe path of the spray as the discharge electrode means, and meansproviding a high voltage field between said discharge electrode meansand said collector electrode. 2. An electrostatic spray paintingapparatus, comprismg, in combination, a support, spray emitting meansmounted on said support for emitting a spray in a path, dischargeelectrode means mounted on said support and electrically insulated fromsaid spray emitting means, said discharge electrode means being locatedin spaced relation to said spray emitting means in the direction inwhich the spray is emitted therefrom and on one side of and adjacent tothe path of the spray, a collector electrode mounted on said support inspaced relation to said discharge electrode means and adjacent to saidspray emitting means, said collector electrode being located on the sameside of and adjacent to the path of the spray as the discharge electrodemeans, means providing a source of high voltage and a low voltagereturn, means connecting said discharge electrode means to said sourceof high voltage, and means connecting said collector electrode to saidlow voltage return.

3. An electrostatic spray painting apparatus claimed in claim 1, whereinthe collector electrode comprises an elongated metallic cylinder, thelongitudinal axis of which is transverse to the path of the spray.

4. An electrostatic spray painting apparatus claimed in claim 1, whereinthe discharge electrode means comprises a plurality of pointed membersarranged in an array pointing perpendicular to and toward the path ofthe spray, and wherein the collector electrode comprises an elongatedmetallic cylinder, the longitudinal axis of which is transverse to thepath of the spray and to the axis of the center one of the pointedmembers of the discharge electrode means.

References Cited in the file of this patent UNITED STATES PATENTSRansburg Dec. 21, 1954 Tuttle et a1. Nov. 8, 1955 Juvinall July 10, 1956Larsen et a1. Oct. 16, 1956 FOREIGN PATENTS Great Britain May 29, 1957

